The development of six distinct classes of neurons and one class of glia in the vertebrate retina requires a complex interplay of cell-intrinsic and cell-extrinsic molecular events. The experiments proposed here will utilize the powerful system of the teleost retina to establish the specific roles and relative hierarchy of molecules reported to function in the development of rod photoreceptors. Since the teleost retina adds new neurons and glia throughout its life, all stages of retinal development are present concurrently. The first set of proposed experiments are designed to discover the hierarchy of expression of a set of transcription factors expressed in the course of rod photoreceptor development. Following their description, overexpression and blocking experiments will establish the role of each factor in controlling rod neurogenesis. The second set of experiments will define the role of secreted growth factors in rod photoreceptor development. Soluble factors including CNTF, EGF, and TGFalpha will be applied to retinal slices and their effects on cell division and differentiation measured. Application of antibodies to block the function of each molecule will further help to elucidate their function. The transcription factors and growth factors present in the teleost retina are found in most vertebrates, including humans. Understanding the mechanisms that cause a dividing progenitor cell to become a particular kind of neuron may become useful in treating human disease, particularly since stem cells have recently been identified in the mammalian central nervous system and human embryonic stem cells have been isolated.